Phase transitions in the antiferroelectric-ferroelectric mixed systems

TL;DR

This paper develops a theoretical model to analyze phase transitions in mixed antiferroelectric-ferroelectric systems like PZT and RADP, accurately predicting transition temperatures based on composition.

Contribution

The paper introduces a self-consistent theoretical approach incorporating random electric fields to describe phase transitions in mixed ferroelectric systems.

Findings

The model accurately fits experimental transition temperatures for PZT and RADP.

Random electric field effects significantly influence phase stability.

The approach can be extended to other mixed ferroelectric systems.

Abstract

Phase diagram of solid solutions of antiferroelectric and ferroelectric materials like PbZr$_{1-x}$Ti$_x$O$_3$ (PZT), Rb$_x$(NH$_4$)$_{1-x}$H$_2$PO$% _4$ (RADP) is calculated at the region $x\leq 0.1$. Antiferroelectric and ferroelectric order parameters (which correspond respectively to the difference and sum of two sublattices ions shifts) were introduced for antiferroelectric host lattice. Small admixture of ferroelectric component was considered as a random electric field source. The influence of this field on both aforementioned order parameters was calculated. Self consistent averaging with calculated random field distribution function made it possible to obtain the system of equations for order parameters of mixed system. The antiferroelectric $T_a$ and ferroelectric $T_c$ phase transition temperature concentrational dependence was expressed through the transition temperatures of the composition and members. The obtained $T_a(x)$ dependence was shown to fit pretty good the observed values for PZT and RADP. The application of the proposed theoretical approach to other types of mixed systems is discussed.